The proposed studies will quantify the kinetics and metabolism of serine during human pregnancy and examine its possible relation to fetal growth by examining such populations with fetal macrosomia and intrauterine growth retardation. It is hypothesized that as gestation advances and as the rates or urea synthesis decline, a significant change in the intrahepatic nitrogen metabolism occurs wherein increased amounts of nitrogen from ureagenic precursors are transferred to synthesize non-essential amino acids such as serine and glycine, and that glucose is a major source of serine carbon. It is further hypothesized that significant amounts of serine and glycine may be transferred to the fetus. Diabetes in pregnancy is characterized by increased protein breakdown, and thus it is expected that there is an increased rate of serine and glycine turnover. The plan of investigation continues to be to study normal pregnant women, pregnant women with insulin dependent diabetes, pregnant women with IUGR fetuses, women undergoing scheduled cesarean sections and non-pregnant controls. The normal pregnant women will be studied serially through pregnancy.